Gut microbiota were affected by age, gut section and antimicrobial treatment but these differences did not affect broiler performance, according to Torok and co-authors. The antibiotics reduced the differences in ileal bacterial communities between individual birds.

The influence of antimicrobial feed additives on commensal post-hatch gut microbiota development and performance were investigated by Dr Valeria Torok of SARDI and University of New England and co-authors there and at the Australian National University. The paper was published in the journal, Applied and Environmental Microbiology, earlier this year.

The researchers explain that they investigated the effects of avilamycin, zinc bacitracin and flavophospholipol on broiler gut microbial community colonisation and bird performance in the first 17 days post-hatch.

Significant differences in gut microbiota associated with gut section, dietary treatment and age were identified by terminal restriction fragment length polymorphism (T-RFLP) although no performance-related differences between dietary treatments were detected.

Similar age-related shifts in the gut microbiota were identified regardless of diet but varied between the ilea and caeca.

Inter-bird variabilities in ileal bacterial communities were reduced – three to seven days post-hatch – in chicks fed with feed containing antimicrobial agents. Avilamycin and flavophospholipol had the most consistent effect on gut microbial communities.

Operational taxonomic units (OTU) linked to changes in gut microbiota in birds on antimicrobial-supplemented diets were characterised and identified.

Some OTUs could be identified to the species level; however, the majority could be only tentatively classified to the genus, family, order or domain level. OTUs 140 to 146 (Lachnospiraceae), OTU 186/188 (Lactobacillus johnsonii), OTU 220 (Lachnospiraceae), OTUs 284 to 288 (unclassified bacterial spp. or Ruminococcaceae), OTU 296/298 (unclassified bacterium or Clostridiales), and OTU 480/482 (Oxalobacteraceae) were less prevalent in the guts of chicks fed antimicrobial-supplemented diets.

Dr Torok and her co-authors add that the identification of key bacterial species influenced by antimicrobial-supplemented feed immediately post-hatch may assist in the formulation of diets that facilitate beneficial gut microbial colonisation and, hence, the development of alternatives to current antimicrobial agents in feed for sustainable poultry production.